The present invention relates to a weld line profiling control method for the arc welding robot.
In effecting fillet welding as shown in FIG. 1a or single-V groove welding as shown in FIG. 1b with a conventional consumable electrode arc welding apparatus, a carriage carrying a welding torch 1, which is capable of weaving motion, is made to run along the groove line, in which a welding bead 2 is deflected when the carriage is incorrectly guided. In order to eliminate this problem, an automatic weld line tracking and profiling controller has been proposed. The controller is provided with an actuator adapted to move the welding torch 1 horizontally along the weaving direction with respect to the weld line by taking advantage of a fact that the respective welding currents or the welding voltages at both laterally extreme positions of the weaving differ from each other when the center of weaving of the welding torch tip is deflected from the weld line, the actuator is controlled so as to make the difference between the respective detected values detected at both laterally extreme positions of weaving zero to form aligned weld beads, and the actuator is controlled also along the vertical direction (direction of the consumable electrode) to always make the detected values constant.
When this profiling method is applied to known cylindrical coordinates robots, polar coordinates robots, Cartesian coordinates robots or articulated robots, the arc welding robot will assume, for example, a structure as shown in FIG. 2.
FIG. 2 shows an example of application of above-mentioned method to an articulated robot, in which a weaving unit 3, a horizontal drive actuator 4 and a vertical drive actuator 5 are mounted on the robot wrist.
Since three actuators for driving three axes in total of two axes of the actuators and one axis of the weaving unit are to be mounted on the robot wrist, the size and the weidht of the drive actuators cause problems. Namely, the increased weight of the working tool increases the load on the robot wrist, which is undesirable from the viewpoint of the durability of the robot wrist. The increased size of the working tool causes difficulty in extending the robot wrist into a narrow position, thereby the weld position is restricted and the versatility of the welding robot is reduced.
This invention is directed to the method for controlling a welding robot which can eliminate those disadvantages.
This invention provides that the three-axes actions of the weaving axis, horizontal actuator and vertical axis actuator, or the two-axes actions of the horizontal and vertical actions are effected by three basic axes for performing the three-dimensional motion of the robot instead of these actuators. More particularly, while the center of weaving is controlled so as to follow a previously taught locus or a locus given by parallely shifting the previously taught locus in a three-dimensional space, the welding current or the welding voltage is detected every time the torch reaches the laterally extreme positions of weaving and compared with the detected value of the preceding laterally extreme position of weaving, the position of the center of weaving is shifted (correcting control) by controlling the three basic axes of the robot both in a direction to cancel the difference between the detected value and the preceding detected value when there is a difference, namely, in a direction to the right or to the left with respect to the direction of movement of the center of weaving (actual weld line), and in a direction to cancel the difference between the mean value of the welding current or the welding voltage detected at the preceding laterally extreme position of weaving and at the instant laterally extreme position of weaving, and the preset value of the welding current or the welding voltage when there is any difference, namely, in an upward or downward direction with respect to the direction of movement of the center of weaving (a direction perpendicular to the weaving direction). As the result, the position of the center of weaving is shifted toward the resultant vector composed of above-mentioned "right" or "left" and/or "up" or "down" vectors. Thus the deviation of the center of weaving from the actual weld line is corrected, and the welding current or the welding voltage is controlled to a fixed value for correct weaving welding.
Other objects of the invention relate to control methods effective in applying the control method of the invention to the teaching playback robot. Those control methods will be described hereinafter with reference to the drawings.